Light guides are used for several kinds of lighting applications. Examples of such applications are LED-backlights for LCD televisions, LCD monitors and cellular phone displays. Light guides are required here to mix the light from several (sometimes colored) small light sources in order to create a homogeneous light emitting area. When the light is sufficiently mixed, the light is usually coupled out of the light guide by the use of a wedge shape, microstructured surface or dots of paint, towards the back of an image to be displayed for a viewer. Any reflection losses should be kept at a minimum.
A general problem of the above mentioned prior art is that the light is not always sufficiently mixed in all regions of the light guiding layer. Such regions may not be used for coupling out light and they should therefore be minimized or preferably omitted by incorporating more efficient light mixing.
US-2006/0146573, for example, discloses a technique for scattering light in a light guide. The scattering is achieved by transmitting light from a light source into a layer, which light is then repeatedly redirected by total internal reflection, i.e. towards a reflective object positioned at a distance from the point where the light is transmitted into the light guiding layer. When light is incident on the reflective object, the light, which has now been sufficiently mixed, is reflected by the reflective object such that the reflected light changes its directional distribution and thereby is emitted from the light guiding layer into a layer with extraction. A disadvantage with the described technique is that part of the reflected light is returned back to the light source. This decreases the efficiency of the system, in particular for small (segmented) backlights.